1. Technological Field of the Invention
The present invention relates to an on-snow tire-testing method, an on-snow tire-testing system, and a road surface for the on-snow testing of tires.
2. Background Art
Heretofore, in testing the performance of tires on snow, generally a test course on which snow has accumulated has been used.
Nevertheless, the aforesaid method is problematic in that testing can be performed only during winter, when snow has fallen.
Testing methods have been considered whereby artificial snow is created by finely pulverizing ice or freezing sprayed water, and this artificial snow is spread on a road surface, but the problem is that large-scale facilities are required for this method.
When testing is performed by spreading this type of artificial snow on the road surface, in order to prevent the snow produced from melting, it is necessary to refrigerate a large road surface, to lay the road surface inside an enclosed structure, and to maintain the air temperature inside the structure below the freezing point.
Further, since the snow cannot be reused once it has melted, it must be disposed of as wastewater. When long-term testing is performed, the snow is melted after the completion of testing and must be disposed of in a sewer system as water, and then artificial snow must be created again for the next set of tests, requiring large quantities water.
The present invention was produced in light of this situation and has an object of offering an on-snow tire-testing method, an on-snow tire-testing system, and a road surface for snow-testing tires, which enables snow testing of tires to be performed at low cost.
The on-snow tire-testing method of the present invention involves testing tires on an artificial snow layer obtained by placing artificial snow in a layered form and cooling the snow. The artificial snow is composed of a granular water-absorbent material that has been made to expand by the addition of water.
In the on-snow tire-testing method according to the present invention, various types of snow tests for tires are performed on the artificial snow layer after it has been cooled. In this way, snow test data for tires can be obtained at any time without requiring snowfall.
Further, since the water is held in the water-absorbent material even if the artificial snow is melted, it returns to the form of artificial snow when cooled and frozen.
The term xe2x80x9ccoolingxe2x80x9d used here means making the artificial snow into a form like that of actual snow, and may involve complete freezing or partial freezing of the artificial snow.
The artificial snow layer may be obtained by placing the artificial snow in a layered form on an ice layer and cooling the snow.
Since the artificial snow changes its form according to the temperature in the same way as actual snow, in order for the artificial snow as a whole to assume a uniform state, it is necessary to reduce temperature irregularities.
By providing an ice layer on the underside of the artificial snow layer, the artificial snow layer as a whole can be maintained at a constant temperature, and snow test data can be obtained with a high degree of reliability with a uniform artificial snow layer.
The ice layer is cooled by means of a cooling device which is arranged on the bottom face of the snow layer and/or the interior of the snow layer.
Even if the air temperature is high (e.g., exceeds 0xc2x0 C.), the melting of the ice layer and artificial snow layer can be prevented, and the initial road conditions can be maintained. Moreover, depending upon the conditions, the ice layer and artificial snow layer can be maintained at a temperature of 0xc2x0 C. or less.
The artificial snow may be compressed and used. By compressing the artificial snow, the artificial snow layer assumes a state similar to that of an actual compressed snowy road, for example, and test data is obtained similar to test data obtained when on-snow testing is performed using an actual compressed-snow road.
Various types of road conditions can be reproduced by increasing or decreasing the amount of compression. For example, various road surface conditions from a soft-compressed snow road to a hard-compressed snow road can be reproduced by increasing or decreasing the amount of compression when compressing the artificial snow. Accordingly, snow test data for the desired road conditions can be obtained.
Testing tires is performed on the artificial snow layer which rotates. Since the tire-testing is performed on a rotating artificial snow layer, testing is simpler than when the tire is installed on a test vehicle and driven, and the snow testing of tires can be performed in a smaller space.
A tire is rotated on the artificial snow layer, which is rotated, and slipping between the artificial snow layer and the tire, which is generated by increasing or decreasing the rotational speed.
For example, by increasing the rotational speed of the tire, and setting the circumferential speed of the tire at higher speed than the speed of movement of the artificial snow layer (the portion in contact with the tire), conditions when driving, when accelerating, etc., can be reproduced.
Further, by reducing the rotational speed of the tire, and setting the circumferential speed of the tire at lower speed than the speed of the movement of the artificial snow layer (the portion in contact with the tire), conditions such as those of deceleration can be reproduced.
The tangential direction of rotation of the artificial snow layer and the direction of the equatorial plane of the tire can be made to differ, and the tire is thereby provided with a slip angle. Snow-testing data when the tire is provided with a slip-angle can therefore be obtained.
By increasing or decreasing the water absorption factor by 10 to 100 times, various road surface conditions can be reproduced. That is, by increasing or decreasing the water added to the granular water-absorbent material by 10 to 100 times the weight (mass) of the water-absorbent material, artificial snow having various states can be obtained, and various road surface conditions similar to actual road surfaces can thereby be reproduced. Accordingly, snow-testing data can be obtained for the desired road surface conditions.
The artificial snow layer is also able to reproduce various road surface conditions by increasing or decreasing the temperature of the artificial snow layer and/or the ice layer. Accordingly, on-snow test data for a desired set of road conditions can be obtained.
The water-absorbent material is preserved and reused. After the completion of testing, the artificial snow, i.e., water-absorbent material, is preserved and can be reused for the next test. Accordingly, it is not necessary to prepare a new water-absorbent material for each test, testing can be performed with a minimal quantity of water-absorbent material, and the cost of testing can be minimized.
The water-absorbent material is preserved in a gel form containing water. Since the artificial snow, i.e., water-absorbent material, is preserved in a gel form containing water, it is not necessary to add water when performing the next test. When the moisture in the gel evaporates due to storage conditions, an amount water equivalent to the amount evaporated is injected.
The on-snow tire-testing system includes an artificial snow layer arrangement device, which arranges artificial snow composed of a granular water-absorbent material made to expand by the addition of water in a layered state, a cooling device, which cools the artificial snow layer, and a tire-testing device, which can rotate and which supports the tires and performs testing on the tires on the artificial snow layer.
The tire-testing device has a tire pressing device, which presses the tire on the artificial snow layer. Thus, the load applied to the tire can be easily changed in comparison with cases where testing is performed by driving a test vehicle on which tires have been installed, and testing can be performed by applying various loads to the tires.
The tire-testing device has a driving/braking device, which exerts a driving force or braking force on the tire. Thus, tests relating to tire driving or braking can be performed, and test data on the driving properties and braking properties can be obtained.
The tire-testing device has a slip-angle applying device, which provides the tire with a slip-angle by causing the tangential direction of the rotation of the artificial snow layer and the direction of the equatorial plane of the tire to differ. Accordingly, the tire can be tested by applying a slip-angle to the tire, and on-snow test data when a slip-angle is applied can be obtained.
A tire moving device moves the tire along the rotational radial direction of the artificial snow layer.
In the case where the artificial snow layer is made to rotate while the tire is pressed against the artificial snow layer, if the position of the tire (position in the radial direction) does not change, the tire will run over and over on the same area of the artificial snow layer, and a rut will be gradually worn in the artificial snow layer, such that the road surface conditions will change. For this reason, by moving the tire along the rotational radial direction of the artificial snow layer, testing can be continued for a longer period of time under constant road surface conditions.
A pressure-rotation device applies pressure to the artificial snow layer while rotating the artificial snow layer. For this reason, the artificial snow layer can be set in conditions similar to those of actual compressed snow road surfaces.
A leveling device levels the surface of the artificial snow layer. The surface of the artificial snow layer can be made uniformly flat by the leveling device without manual operation, and accordingly tires can be tested on an evenly flat artificial snow layer.
When the tire is driven over and over in the same area of the artificial snow layer, a rut is gradually worn in the artificial snow layer, and road surface conditions will change, but the road surface can be leveled for each test, or testing can be performed while the road is leveled.
The on-snow tire-testing system may include a snow removal device. The artificial snow that has been arranged on the artificial snow arrangement device can be removed by the snow removal device. For example, this device can be used when the artificial snow is to be stored in another place after testing, or when it is to be replaced with artificial snow in a different state.
The on-snow tire-testing system may also include a snowfall device, which causes artificial snow to fall on the artificial snow layer. If artificial snow is made to fall while the artificial snow layer arrangement device is made to rotate, for example, an artificial snow layer can be easily formed on the artificial snow layer arrangement device, and road surface conditions in which new snow has accumulated can be obtained.
A road surface for on-snow testing of tires has as its uppermost portion an artificial snow layer which is caused to swell by the addition of water to a granular water-absorbent material, and the artificial snow layer is cooled. Accordingly, various types of on-snow testing of tires can be performed on a cooled artificial snow layer, and on-snow testing of tires can be performed at any time without requiring snowfall.
Since the state of artificial snow varies according to the temperature, in the same way as with actual snow, it is necessary to reduce temperature unevenness in order to make the entire artificial snow layer into a uniform state.
By placing an ice layer on the underside of the artificial snow layer, the artificial snow layer as a whole can be maintained at a roughly even temperature, and it is possible to obtain on-snow testing data having high reliability with the artificial snow layer in a uniform state.
Finally, testing can be performed by installing a tire anti-slip device on the tire. It is therefore possible to obtain on-snow testing data for tires to which an anti-slip device has been attached.